Heart rate monitors that can be worn in a belt attached around a person's chest have become popular by professional athletes as well as runners and others engaged in physical exercises where the heart rate provides information about the effects of a training program and allows a user to exercise according to a plan in order to optimize efficiency and measure results of the training program. Recently, heart rate monitors that can measure heartrate at the wrist has also become available. It is well known that additional information can be obtained by measuring ventilation and/or respiration, but devices capable of performing such measurements are bulky and mostly used in laboratories, for example spirometers and cannulas, which a person has to breathe through while running on a treadmill or using a stationary exercise bike.
Alternatives do exist, for example in the form of piezoelectric sensors, magnetic sensors and nasal/oral thermocouples, as well as chest belts with resistivity dependent on tension. The different alternatives are all associated with various disadvantages, such as bulkiness, inaccuracy, discomfort etc., and they are not commonly used during regular exercises.
Consequently, the information that can be derived from measurement of respiration or ventilation has been unavailable to a person during training, and impossible to utilize as a means of optimizing training efficiency or measuring the effects of a training program over time.
With respect to terminology it should be noted that while respiration normally refers to the exchange of gases, primarily O2 and CO2, ventilation refers to the transportation of air into and out of the lungs through inhalation and exhalation. These terms are sometimes used interchangeably, but in the present description an attempt has been made to maintain a certain consistency in their respective use. However, there are clear physiological links between the two and certain parameters of one may be calculated or estimated based on parameters of the other. Also, the term respiratory rate will be used because of its establishment through convention, even if the correct term is ventilatory rate.